A novel helicon plasma source for negative ion beams for fusion Ivo Furno 1 R. Agnello 1, B. P. Duval 1, C. Marini 1, A. A. Howling 1, R. Jacquier 1, Ph. Guittienne 2, U. Fantz 3, D. Wünderlich 3, A. Simonin 4, and S. Béchu 5 1 Ecole Polytechnique Fédérale de Lausanne (EPFL), SPC, CH-1015 Lausanne, Switzerland 2 Helyssen, Route de la Louche 31, CH-1092 Belmont-sur-Lausanne, Switzerland 3 Max-Planck-Institut fuer Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany 4 CEA, IRFM, F-13108 St Paul lez Durance, France 5 LPSC, Université Grenoble-Alpes, CNRS/IN2P3, F-38026 Grenoble, France 5 th International Symposium on Negative Ions, Beams and Sources 12 th - 16 th September 2016, Oxford, UK
Requirements for DEMO neutral beam are challenging and R&D is required DEMO 1 Species D - Beam Energy [kev] 800 Current [A] 34 Filling pressure [Pa] 0.2 Beam on time [s] 7200 Extracted e-/d- fraction <1 Neutralization efficiency >0.65 [1] P. Sonato et al., Conceptual design of the beam source for the DEMO NBI, submitted NJP 0
Requirements for DEMO neutral beam are challenging and R&D is required DEMO 1 Species D - Beam Energy [kev] 800 Current [A] 34 Filling pressure [Pa] 0.2 Beam on time [s] 7200 Extracted e-/d- fraction <1 Neutralization efficiency >0.65 Photoneutralization concept on Cybele 0
Requirements for DEMO neutral beam are challenging and R&D is required DEMO 1 Species D - Beam Energy [kev] 800 Current [A] 34 Filling pressure [Pa] 0.2 Beam on time [s] 7200 Extracted e-/d- fraction <1 Neutralization efficiency >0.65 Photoneutralization concept on Cybele 0
Requirements for DEMO neutral beam are challenging and R&D is required DEMO 1 Species D - Beam Energy [kev] 800 Current [A] 34 Filling pressure [Pa] 0.2 Beam on time [s] 7200 Extracted e-/d- fraction <1 Neutralization efficiency >0.65 Can helicon sources be an option? Physics Technology Photoneutralization concept on Cybele 0
Outline The Resonant Antenna Ion (RAID) device at SPC the birdcage resonant antenna OES and Langmuir probe measurements highly dissociated H 2 and D 2 plasmas presence of negative ions Summary and outlook 1
The Resonant Antenna Ion Device (RAID) at SPC 6 water-cooled coils water-cooled vacuum vessel (length 2m, diam. 0.4m) Birdcage resonant antenna Extensive diagnostic access 2
CW10kW birdcage resonant antenna 9 water-cooled copper legs D int =13 cm L = 15 cm Water OUT Water IN 3 nf Mica Capacitors 3
The birdcage antenna on RAID Faraday shield Ceramic tubing RAID end flange End window 13.56 MHz RF IN 4
The birdcage antenna on RAID Faraday shield Ceramic tubing RAID end flange Metal screens End window 13.56 MHz RF IN 4
The birdcage antenna in a nutshell RF : 1-100 MHz Balanced, high-pass, passive filter ladder network conducting legs capacitors V RF C eq L eq R eq Each resonant frequency Real impedance ω m L 1 eq C eq Antenna equivalent circuit (lumped elements ) ω N-1 resonant frequencies m 1 = C M + 2Lsin m 2N 2 π m=1, 2,, N-1 5
RAID antenna impedance 160 Real impedance 140 120 Screen at 4 cm 1 MHz Screen at 2 cm 100 [Ohms] 80 60 40 20 0 5 6 7 8 9 10 11 12 13 14 15 [MHz] 13.56 MHz 6
Birdcage antennas efficiently produce helicon plasmas Argon, B=500 Gauss, p=10-2 mbar hysteresis transition to helicon regime ignition inductive coupling Ph. Guittienne et al., J. Appl. Phys. 98, 083304 (2005) 7
A 3 kw, 0.3 Pa,120Gauss, H 2 plasma Birdcage antenna Water IN water-cooled end plate 8
Diagnostics: Langmuir probe, OES y z x Compensated LP high throughput spectrometer + detector optical fiber bundle 9
Absolute OES in multi-chord geometry 19 viewing lines x 2 Cylindrical symmetry Graphite dump C. Marini et al., Spectroscopic characterization of H 2 and D 2 helicon plasmas generated by a resonant antenna for neutral beam applications in fusion, in preparation for NF 10
Profiles are Abel inverted and analyzed with the collisional radiative code YACORA 1 11
Profiles are Abel inverted and analyzed with the collisional radiative code YACORA 1 YACORA profiles of H, H 2, H -, H +, H 2+, n e, T e [1] D. Wunderlich et al., J. Quant. Spectros. Radia. Transfer 110, 62-71 (2009) 11
Peaked T e and n e profiles are observed from OES and LP measurements A. Simonin et al., Negative ion source development for a photoneutralization based neutral beam system for future fusion reactors, to appear in NJP 12
Peaked T e and n e profiles are observed from OES and LP measurements Favorable for negative ion production by dissociative attachment H 2 (v) + e H - + H 12
H 2 plasmas are characterized by high dissociation degree and negative ions Ratio atomic-molec. density 13
H 2 plasmas are characterized by high dissociation degree and negative ions Ratio atomic-molec. density core transition edge 13
Both H 2 and D 2 plasmas are efficiently produced at different RF powers Hydrogen Deuterium 2.5 minimum power 14
Both H 2 and D 2 plasmas are efficiently produced at different RF powers Hydrogen Deuterium 2.5 maximum power 14
n e increases with RF power while T e is almost constant Deuterium core transition edge 15
Isotopic effect: D 2 has higher dissociation and ionization degrees than H 2 increasing with RF power Deuterium core transition edge 16
With RF power, the negative ion population increases in H 2, rolls over (?) in D 2 Hydrogen Deuterium 17
Summary The RAID facility is operational at SPC H 2 and D 2 plasmas are efficiently produced at different RF power, low magnetic field and low pressures OES and LP measurements show peaked n e and T e profiles a high dissociation degree a negative ion population Scaling with powers is encouraging for applications as a negative ion source for fusion in a Cybele-like geometry 18
Open physics questions Outlook helicon wave physics source optimization larger power Upgraded and new diagnostics Microwave interferometer Laser photo-detachment comparison with OES Laser induced fluorescence 3D Langmuir probes 3D profiles Magnetic probes helicon waves physics Installation of the resonant antenna on the Cybele to test extraction of negative ions 19